In its most commonly practiced form silver halide photography employs a film in a camera to produce, following photographic processing, a negative image on a transparent film support. A positive image for viewing is produced by exposing a photographic print element containing one or more silver halide emulsion layers coated on a reflective white support through the negative image in the camera film, followed by photographic processing. In a relatively recent variation negative image information is retrieved by scanning and stored in digital form. The digital image information is later used to expose imagewise the emulsion layer or layers of the photographic print element.
Whereas high bromide silver halide emulsions are the overwhelming commercial choice for camera films, high chloride cubic grain emulsions are the overwhelming commercial choice for photographic print elements. It is desired in high chloride emulsions for color paper applications to obtain high photographic speed at the desired curve shape. While it has been common practice to avoid or minimize the incorporation of iodide into high chloride grains employed in color paper, it has been recently observed that silver iodochloride cubical grains can offer exceptional levels of photographic speed where iodide is incorporated in such emulsion gains in a profiled manner. Chen et. al. in U.S. Pat. No. 5,547,827; Chen et. al. in U.S. Pat. No. 5,550,013; Chen et. al. in U.S. Pat. No. 5,605,789; Chen et. al. in U.S. Pat. No. 5,726,005; Edwards et.al. in U.S. Pat. No. 5,728,516; Chen et. al. in U.S. Pat. No. 5,736,310; Budz et.al. in U.S. Pat. No. 5,783,372 and Edwards et.al. in U.S. Pat. No. 5,792,601 disclose highly sensitive silver iodochloride cubical emulsions with low levels of iodide located in the exterior portions of the grains. The interior portions of such grains can be prepared by employing any convenient high chloride cubical grain precipitation procedure. The emulsion grains thus formed then serve as hosts for further growth. Once a host grain population has been prepared, an increased concentration of iodide is introduced into the emulsion to form the region of the grains containing maximum iodide concentration. The source of iodide ion can be silver iodide grains or any iodide-releasing agent, but it is typically disclosed that iodide is preferably introduced alone as an aqueous solution of an alkali metal iodide salt. This is followed by double-jet introduction of silver nitrate and alkali metal chloride solutions at conventional molar addition rates, constant or ramped, till the exterior portion is grown to the desired size.
Chow U.S. Pat. No. 5,549,879 discloses a pulsed flow double jet technique for preparing silver halide grains. Chow discloses introducing an aqueous silver nitrate solution from a remote source by a conduit which terminates close to an adjacent inlet zone of a mixing device, which is disclosed in greater detail in Research Disclosure, Vol. 382, February 1996, Item 38213. Simultaneously with the introduction of the aqueous silver nitrate solution and in an opposing direction, aqueous halide solution is introduced from a remote source by a conduit which terminates close to an adjacent inlet zone of the mixing device. The mixing device is vertically disposed in a reaction vessel and attached to the end of a shaft, driven at high speed by any suitable means. The lower end of the rotating mixing device is spaced up from the bottom of the vessel, but beneath the surface of the aqueous silver halide emulsion contained within the vessel. Baffles, sufficient in number to inhibit horizontal rotation of the contents of the vessel are located around the mixing device.
Chow teaches operating the described apparatus in a "pulse flow" manner comprising the steps of: (a) providing an aqueous solution containing silver halide particles having a first grain size; (b) continuously mixing the aqueous solution containing silver halide particles; (c) simultaneously introducing a soluble silver salt solution and a soluble halide salt solution into a reaction vessel of high velocity turbulent flow confined within the aqueous solution for a time t, wherein high is at least 1000 rpm; (d) simultaneously halting the introduction of the soluble silver salt solution and the soluble halide salt solution into the reaction for a time T wherein T&gt;t, thereby allowing the silver halide particles to grow; and (e) repeating steps (c) and (d) until the silver halide particles attain a second grain size greater than the first grain size. Chow teaches the pulse flow technique to permit easier scalability of the precipitation method. There is no disclosure of use of such pulse flow technique to prepare profiled silver iodochloride emulsion grains.